Underactive neural circuits become more sensitive to neurotransmitters, increasing their potential influence when activity resumes.

“Whereas, if a neural circuit is very quiet, it's not activated for a period of time, maybe your leg is in a cast for instance, and you're not activating your quadricep and calves very much, well when that cast comes off, sure, the muscle might be atrophied but the nerves that connect to that muscle are actually in a position to influence that muscle even more once you start using that muscle or those muscles, because whatever neurotransmitter is released now has the opportunity”